In a cellular network a wireless terminal communicates with a base station over a radio or air interface using radio frequencies which are licensed to operator(s) of the cellular network. For example, in a radio technology known as Long Term Evolution (LTE), a Third Generation Global Partners (3GPP) standardized radio access technology, a wireless terminal known as a user equipment (UE) communicates over a licensed frequency spectrum with a base station known as an eNodeB or eNB. In view of increasing traffic demand, cellular operators need more radio frequency spectrum than that presently licensed for their particular radio access technology.
Although a licensed spectrum is preferred by the cellular operators to provide guaranteed quality of service (QoS) to the user, an unlicensed spectrum may be considered as an effective complement to the licensed spectrum. Examples of unlicensed spectrum include Wi-Fi and Industrial, Scientific, and Medical (ISM) radio frequency bands.
Wi-Fi, also spelled Wifi or WiFi, is a local area wireless technology that allows an electronic device to exchange data or connect to the internet using 2.4 GHz UHF and 5 GHz super high frequency (SHF) radio waves. The Wi-Fi Alliance defines Wi-Fi as any “wireless local area network (WLAN) products that are based on the Institute of Electrical and Electronics Engineers' (IEEE) 802.11 standards”. The ISM bands are reserved internationally for the use of radio frequency (RF) energy for industrial, scientific and medical purposes other than telecommunications. The ISM bands are defined by the International Telecommunication Unit (ITU-R) in 5.138, 5.150, and 5.280 of the Radio Regulations. Table 1 shows that the rules and regulation for using the ISM bands (e.g., 2.4 GHZ and 5 Ghz) are not standardized worldwide.
TABLE 1USE OF ISM BANDS IN SELECTED REGIONS2.4 GHz5150-52505250-53505470-57255725-5850USALegacy SystemsWi-Fi, BT, cordless, . . .Wi-FiWi-FiRulesProtectingN/AN/A*DFS/TPCNo DFSincumbentCo-existFCC Part 15.247, 153.401-407, max Tx power and emission maskwith LegacyEULegacy SystemsWi-Fi, BT, cordless, . . .Wi-FiIn planning, Non-RulesProtectingN/AIndoor onlyIndoor only for 5250-5350, DFS/TPCspecific SRD mayincumbentoperate at 25 mW eirpCo-existLBT, max Tx power and emission maskwith LegacyChinaLegacy SystemsWi-Fi, BT, cordless, . . .Wi-FiTBDLightly licensed,Wi-Fi, P2MPRulesProtectingN/AIndoor onlyIndoor only,N/AincumbentDFS/TPCCo-existMax Tx power and emission maskMax EIRP: 25 mW, 2 Wwith LegacyJapanLegacy SystemsWi-Fi, BT, cordless, . . .Wi-FiWi-FiDSRC (5770-5850), ISMequipment (no radio com)RulesProtectingN/AIndoor onlyIndoor onlyDFS/TPCN/Aincumbentwith DFS/TPCCo-existLBT, Max. conducted power and antenna gain, emission mask defined for each systemISM, DSRC: Max.with Legacyconducted power andEIRP, emission maskKoreaLegacy SystemsWi-Fi, BT, cordless, . . .Wi-FiWi-Fi (5470-5650),Wi-Fi (5725-5825),broadcasting relayDSRC(5835-2855)system(5650-5725)RulesProtectingN/AIndoor onlyDFS/TPCDFS/TPC (5470-5650)N/AincumbentCo-existMax. conducted power and antenna gain, spurious emission defined for each systemwith Legacy
Use of unlicensed spectrum by a wireless terminal which is suited for use in cellular network may be complicated. If, for example, LTE is deployed in unlicensed spectrum (e.g. 2.4 GHz ISM), coexistence with existing users of the unlicensed spectrum (e.g., IEEE 802.11ac . . . Wi-Fi) needs to be carefully considered to ensure that existing users of the shared unlicensed spectrum are not negatively impacted by the use of the unlicensed spectrum by LTE, e.g., by LTE wireless terminals.
Wi-Fi uses a CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) to avoid collisions between transmitting nodes by transmitting only when the channel is sensed to be “idle”. CSMA is based on the principle of “sense before transmit” or “listen before talk” (LBT). The node wanting to “talk” determines that the channel is idle by first listening to the shared spectrum (e.g., listening for wireless signals in a wireless network) to determine whether another node is transmitting or not. If another node was heard, the listening node will wait for a period of time for the transmitting node to stop transmitting before listening again for a free communications channel. If the listening node determines the shared spectrum as being clear the listening node begins its transmission on the shared spectrum.
An LTE user equipment (UE) uses a RACH (Random Access Channel) to gain access to network resources when in an idle state. The RACH is used to initially synchronize the UE's transmission with the eNB. It is a shared channel that is used by all UEs to access the network. A feature of a RACH channel is that messages are not scheduled. There is no certainty that only a single device makes a connection attempt at one time, so collisions can result.
In LTE, cell synchronization is the early step taken by a UE when it attempts to camp on any cell. From the synchronization process, the UE acquires the Physical Cell Identity (PCI), time slot, and frame synchronization of that cell, which will enables the UE to decode and read fundamental data (e.g. PCFICH, PDCCH etc) and UE-specific (PDSCH) data from the cell. If the UE is attempting to acquire/tune a specific band/channel, the UE first finds the primary synchronization signal (PSS). The primary synchronization signal (PSS) is located in the last OFDM symbol of first time slot of the first subframe (subframe 0) of the radio frame. This enables the UE to be synchronized on subframe level. The PSS is repeated in subframe 5, which means UE is synchronized on 5 ms basis since each subframe is 1 ms. From the PSS the UE is also able to obtain a physical layer identity (0 to 2). In another step the UE finds the secondary synchronization signal (SSS). The SSS symbols are also located in the same subframe of PSS but in the symbol before PSS. From the SSS the UE is able to obtain physical layer cell identity group number (0 to 167). Using both the physical layer identity and the cell identity group number, the UE determines the PCI for the cell to which the UE is tuned. In LTE there are 504 PCIs allowed and are divided into unique 168 cell layer identity groups, where each group consist of three physical layer identities. Assuming physical layer identity=1 and cell identity group=2 then the PCI for given cell is determined from Expression 1.PCI=3*(Physical layer cell identity group)+physical layer identity=3*2+1=7  Expression 1:
It is expected that there will be at least two differentiating use cases regarding how the UE will access unlicensed radio frequency bands. A first use case is also known as the “Non-Stand Alone” case; a second use case is also known as the “Stand Alone Unlicensed” case.
In the first case (“Non-Stand Alone” case) the UE will always be connected to the LTE network via a P-Cell (Primary Cell). The P-Cell operates on spectrum licensed to the operator. The P-Cell provides the UE with configuration data regarding how and when the UE will access the RF resources of the unlicensed band. The resources of the unlicensed band will be configured as an LTE eNB and may be considered as a S-Cell (Secondary or Small Cell). In the first use case, the P-Cell may either be co-located with the S-Cell (as shown in FIG. 1A), or the P-Cell and S-Cell may not be co-located but with the S-Cell in the coverage of the P-Cell and with the S-Cell and P-Cell have some logical connection (as shown in FIG. 1B).
In the second use case (“Stand Alone Unlicensed” case) the UE may, or may not, be connected to the LTE network. The resources of the unlicensed band may be configured as an LTE eNB and may be considered by the UE as a U-Cell (Unlicensed Cell) operating in spectrum that is not licensed to the operator. The U-Cell may have a connection to an operator's network (via a direct connection or via an internet connection) [as shown in FIG. 2A]; may have no connection to an operator's network [as shown in FIG. 2B]; or may have an internet connection. As shown in FIG. 2B, the U-Cell may be within P-cell coverage but there is no direct connection (wired or wireless interface) between the U-Cell and the P-Cell. The P-Cell of FIG. 1B is able to exert forms of control and access with respect to the U-Cell that are not otherwise available with the same latency in the FIG. 2B case.
It is expected that for the first case (“Non-Stand Alone” case) the P-Cell will provide the UE with all the necessary information regarding access to the S-Cells operating on unlicensed spectrum in the P-Cell coverage area. This information may be either broadcasted by the P-Cell (e.g., via system information block (SIB) message), or the P-Cell may directly configure the UE (e.g., via a Radio Resource Control (RRC) message).
It is expected that for the second use case (“Stand Alone Unlicensed” case) the UE will have been provisioned with Regional Specific Rules regarding how the UE may access a standalone U-Cell operating on unlicensed spectrum. The provisioning may have been done at time of UE manufacture, or may have been done by the LTE network (at some previous connection with the network), or may have been done at time of UE manufacture and then subsequently updated by the LTE network.
One of the key differentiators between the first case (“Non-Stand Alone” case) and the second use case (“Stand Alone Unlicensed” case) is that in use case 2 the UE may not have network connection to obtain guidance on how to access the unlicensed U-Cell. Thus the UE must rely upon pre-provisioned information or information provided outside the cellular air interface regarding the rules for access to the unlicensed bands per each region. In addition the UE must rely on its location determination mechanism to further determine what pre-provisioned regional rules should be applied to access the unlicensed band.
Depending on the regulatory conditions of a specific region, the use of radio frequency (RF) resources in an unlicensed band may require that a UE always use specific RF resource access rules and RF resource transmit (Tx) power settings. In one example, when using the ISM bands, the use a CSMA/CA approach as a means to co-exist with legacy systems such as Wi-Fi and Bluetooth may be required. If the regulatory conditions of a region do not require the use of CSMA/CA to access the RF resources of an unlicensed band, the UE may still want to use CSMA/CA access to ensure that fair or efficient usage of the resources if other users are currently active on the band. However, if there are no other active users in the unlicensed band in a region where the regulatory conditions do not require the use of CSMA/CA, then the UE may want to not use CSMA/CA, and instead use a LTE access protocol. In another example, the use of TV White Space bands (TVWS) may require specific Tx power settings. Furthermore, it would be useful to have a single standardized solution or algorithm to enable a UE to roam internationally and still take advantage of unlicensed LTE spectrum despite the varying regulatory landscape of different countries.